Burning smell

Ok here my concern yesterday I was driving home
from work coming up highway I got a burning
smell into car so when I got off highway exit I
opened hood looked and seen parts of my
serpentine belt was ripped up so I immediately
took car to mechanic right down road from exit off
highway he looked it all over and said nothing
looks like it seized up that the belt went bad so he
fixed it now on my way home I could still smell that
burning smell once I got home I looked under hood
belt looked fine everything looked like it was
running smoothly now today I drove car back on
highway and I could smell the burning smell lightly
I went back to garage they looked it over again and
said everything looks great that it could be some
residue from old belt burning off or piece of belt
got on exhaust and is burning off I'm just very
concerned cause i drive car everyday on highway I
don't want it to break down or catch fire or
something but before this the car ran awesome
can anyone tell me if it should be OK or if it
something else the a compressor seems to be
working good to it turns on and off fine and
everything